Method and apparatus for removeably coupling a heat rejection device with a heat producing device

ABSTRACT

A method and apparatus for removeably coupling a heat rejecting device with a heat producing device, wherein a thermal interface material having a predetermined phase change temperature is between the heat rejecting device and the heat producing device, the method comprising: configuring the heat rejecting device to include at least one heating element; and energizing the at least one heating element for a predetermined amount of time through at least one electrical contact, wherein a current applied to the at least one heating element heats the at least one heating element until the thermal interface material substantially reaches the predetermined phase change temperature. The at least one heating element is located on an interface surface in contact with the thermal interface material, although alternatively on an opposite surface, or within the apparatus.

RELATED APPLICATION

[0001] This Patent Application claims priority under 35 U.S.C. 119 (e)of the co-pending U.S. Provisional Patent Application, Serial No.60/420,557 filed Oct. 22, 2002, and entitled “VAPOR ESCAPE MICROCHANNELHEAT EXCHANGER WITH SELF ATTACHMENT MEANS”. The Provisional PatentApplication, Serial No. 60/420,557 filed Oct. 22, 2002, and entitled“VAPOR ESCAPE MICROCHANNEL HEAT EXCHANGER WITH SELF ATTACHMENT MEANS” isalso hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a method and apparatus for attaching anddetaching two or more devices to one another in general, andspecifically, to a method and apparatus for removeably coupling a heatrejection device to a heat producing device.

BACKGROUND OF THE INVENTION

[0003] High power integrated circuits have evolved in recent yearstowards ever increasing transistor density and clock speed. The resultof this trend is a rapid increase in the power and heat density ofmodern microprocessors and an emerging need for new coolingtechnologies. One aspect of this problem is addressed by the developmentof novel heat rejection devices or structures including, but not limitedto heat pipes, fin-arrays with fans or microchannel liquid coolers. Allof these structures are efficient at transporting the heat to someremote location. In all of these cases, heat is deposited in a liquid,solid or gas medium and that medium provides transport of the heat byconduction or convection.

[0004] A more fundamental aspect of this problem relates to the transferof the heat from an electronic device through a coupling thermalinterface into the heat rejection device. A schematic of thisconfiguration is illustrated in FIG. 1A. The thermal interface betweenthe heat rejection device and the heat producing electronic device is acritical layer in this overall system. In particular, the interface'scharacteristics can place severe limits on the overall performance ofthe system, regardless of the heat removing capabilities of the heatrejection device or structure. Typically, thermal interfaces include athin film of material that is positioned between contacting surfaces ofthe heat producing device and the heat rejection structure, whereby theheat producing device and the heat rejection structure may or may not bemade of the same material having a same thermal expansion coefficient.

[0005] There are cases in which the heat producing device and the heatrejection structure are made of different materials and thus havedifferent thermal expansion coefficients. One example is where the heatproducing device is made from Silicon and the heat rejection device ismade from Copper. In these cases where the heat rejection structure hasa different thermal expansion coefficient than the electronic device,the thermal interface material must be able to maintain contact andallow shear between both of the surfaces. Thermal greases are often usedin such applications, as the grease is “liquid” and can be shearedwithout losing contact with either surface. In addition, the thermalgrease has a high viscosity such that the surfaces of the heat producingdevice and heat rejection device do not separate or slide laterally whenthe heat producing device is operating. FIGS. 1A and 1B illustrate aCopper heat rejection device attached to the backside of a Silicon chipwith a layer of thermal grease in between. As shown in FIG. 1B, thecopper is heated and expands due to the temperature being produced fromthe Silicon chip. Since Copper has a larger thermal expansioncoefficient than Silicon, the thermal grease in between the chip and therejection device allows the heat rejection device to expand withoutexerting force on the Silicon, as shown in FIG. 1B.

[0006] In addition, it is possible to engineer a high performance heatrejection structure that has a thermal expansion coefficient whichmatches the heat producing device. Both structures having the samethermal expansion coefficient allows thermal interface material to beused, whereby the thermal interface material does not shear. Examples ofthese thermal attaches such as thin, solid adhesives, include, but arenot limited to metal layers, eutectic, solder and direct fusion bonding.The thermal resistance of these thin solid layers is lower than thermalgrease. In addition, the thermal resistance for metal attaches can besignificantly lower than thermal grease.

[0007] However, use of a thin, solid adhesive between the Silicon deviceand the Copper heat rejection device causes the Copper-Silicon sandwichto curl due to the thermal expansion coefficient mismatch between theSilicon heat producing device and the Copper heat rejection device. Thisis shown in FIG. 1C. As shown in FIG. 1C, the differential thermalexpansion between the Copper heat rejection device and the Silicon chipresults in a bimetal bending that causes some of the bumpbonds betweenthe Silicon chip and the circuit board to fail.

[0008] An issue with using a metal, eutectic, or fusion bond between theSilicon heat producing device and the metal-type heat rejection deviceis the high temperature needed to form the bond between the two devices.Melting the metal or the eutectic thermal interface requirestemperatures that exceed the thermal limitations of the electronicdevice or its supporting package. This is a reason that a eutectic orsolder bond is not in wide use as a thermal interface attach between anelectronic device and a heat rejection device, despite the performanceadvantages of such an interface. In addition, melting the metal thermalinterface renders the thermal interface between the heat producingdevice and the heat rejecting device to be permanent and non-reworkable.Thus, use of a metal or eutectic as a thermal attach is not currently apreferred material in the industry for applications requiring repeatedremoval and attachment of a heat rejecting device to a heat producingdevice.

[0009] What is needed is a method and apparatus for easily coupling aheat rejection device with a heat producing electronic device having athermal interface therebetween, whereby the thermal interface has a verylow thermal resistance. What is also needed is a method and apparatusfor enabling a heat rejection device to be removeably coupled with aheat producing electronic device, whereby the heat rejection device isreworkable and can be easily removed from the electronic device usinghigh heating temperatures without damaging the electronic device or thepackaging and surrounding electronics.

SUMMARY OF THE INVENTION

[0010] In one aspect of the invention, a method of removeably coupling aheat rejecting device to a heat producing device comprising configuringat least one heating element. The method including applying a thermalinterface material between the heat rejecting device and the heatproducing device. The thermal interface material is configured to allowengagement and disengagement of the heat rejecting device therewithabove a predetermined temperature. The method includes applying acurrent to the heating element, via at least one electrical contact, fora predetermined amount of time, wherein the heating element heats thethermal interface material above the predetermined temperature. Themethod further comprises positioning the heat rejecting device at apredetermined location with respect to the heat producing device. Thethermal interface material undergoes a phase change between a firsttemperature below the predetermined temperature and a second temperatureabove the predetermined temperature. Engagement between the heatrejecting device with the heat producing device further comprisespressing the heat rejecting device and the thermal interface materialagainst one another until the temperature of the thermal interfacematerial is substantially at the first temperature. Disengagement of theheat rejecting device with the heat producing device further comprisesremoving the heat rejecting device and the thermal interface materialagainst one another when the temperature of the thermal interfacematerial is substantially at the second temperature. The at least oneheating element is located on an interface surface in contact with thethermal interface material, although alternatively on an oppositesurface, or within the apparatus. The heating element heats the thermalinterface material in predetermined zone locations. The heating elementapplies heat to the thermal interface material in a substantiallyuniform manner. The heating element applies heat to the thermalinterface material by a plurality of heat pulses, each heat pulse beingof a predetermined time duration.

[0011] In another aspect of the invention, a heat rejector device iscoupled to an interface material. The heat rejector device is secured tothe interface material in a first phase state and is configured to beremoveable from the interface material in a second phase state. The heatrejector device comprises at least one heating element which applies apredetermined amount of heat to the interface material such that theinterface material undergoes a phase change from the first phase stateto the second phase state in response to the predetermined amount ofheat applied thereto by the heating element. The thermal interfacematerial undergoes a phase change between a first temperature, which isbelow the predetermined temperature, and a second temperature, which isabove the predetermined temperature. The thermal interface materialengages the heat rejecting device by being pressed against the heatrejecting device until the thermal interface material reaches to thefirst temperature. The thermal interface material disengages the heatrejecting device by removing the heat rejecting device and the thermalinterface material from one another when the thermal interface materialis at the second temperature. The at least one heating element isconfigured to be in contact with the thermal interface material,although the at least one heating element is alternatively positioned ona surface of the heat rejector device opposite of the thermal interfacematerial or within the heat rejector device. The at least one heatingelement heats the thermal interface material in predetermined zonelocations, in a substantially uniform manner or by a plurality of heatpulses, whereby each heat pulse is of a predetermined time duration. Theheat rejector device further comprises at least one electrical contactpositioned on a predetermined surface, wherein the current is appliedthrough the at least one electrical contact.

[0012] In another aspect of the invention, an assembly for removeablycoupling a heat rejecting device to a heat producing device, wherein athermal interface material having a predetermined phase changetemperature is applied between the heat rejecting device and the heatproducing device. The assembly comprises means for holding an interfacesurface of the heat rejecting device in contact with the thermalinterface material, wherein at least one heating element configured onthe interface surface is in contact with the thermal interface material.The assembly comprises means for energizing the heating element for apredetermined amount of time, wherein the at least one heating elementtransforms the thermal interface material to undergo a phase change thethermal interface material substantially reaches the predetermined phasechange temperature. The interface material is in the first phase statewhen it is below a predetermined phase change temperature. The interfacematerial is in the second phase state when it is above the predeterminedphase change temperature. The interface material undergoes the phasechange between the first phase state and the second phase state withinan appropriate amount of time. The at least one heating element heatsthe interface material in predetermined zone locations, in asubstantially uniform manner, and/or a plurality of heat pulses, eachheat pulse is of a predetermined time duration. The at least one heatingelement is configured to be in contact with the interface material,positioned on a surface of the heat rejector device opposite of theinterface material, or positioned within the heat rejector device. Theheat rejector device including at least one electrical contactpositioned on a predetermined surface, wherein the current is appliedthrough the at least one electrical contact.

[0013] In another aspect of the invention, a method of removeablycoupling a heat rejecting device with a heat producing device, wherein athermal interface material having a predetermined phase changetemperature is applied between the heat rejecting device and the heatproducing device. The method comprising: configuring the heat rejectingdevice to include at least one heating element. The method comprisesenergizing the heating element for a predetermined amount of time,wherein a current applied to the heating element heats the heatingelement until the surface of the thermal interface materialsubstantially reaches the predetermined phase change temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1A illustrates a Copper heat rejection device attached to thebackside of a Silicon chip with a layer of thermal grease in between.

[0015]FIG. 1B illustrates a Copper heat rejection device attached to thebackside of a Silicon chip with a layer of thermal grease in between andexpanding due to heating.

[0016]FIG. 1C illustrates a Copper heat rejection device attached to thebackside of a Silicon chip with a layer of thermal grease in between andundergoing bi-metal bending.

[0017]FIG. 2A illustrates a general schematic of a heat rejector deviceseparated from a heat producing device in accordance with the preferredembodiment of the present invention.

[0018]FIG. 2B illustrates a general schematic of a heat rejector devicecoupled to a heat producing device in accordance with the preferredembodiment of the present invention.

[0019]FIG. 3A illustrates a schematic of a preferred coupling method inaccordance with the present invention.

[0020]FIG. 3B illustrate a schematic of a preferred coupling method inaccordance with the present invention.

[0021]FIG. 4 illustrates a flow chart describing the method of couplingthe heat rejecting device with the heat producing device.

[0022]FIG. 5 illustrates a flow chart describing the method of removingthe heat rejecting device with the heat producing device.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0023]FIG. 2A illustrates a general schematic of a heat rejector deviceseparated from a heat producing device in accordance with the preferredembodiment of the present invention. FIG. 2B illustrates a generalschematic of a heat rejector device coupled to a heat producing devicein accordance with the preferred embodiment of the present invention.

[0024] In particular, FIG. 2A shows a heat producing device 100, such asan electronic device that is coupled to a circuit board 99 by an arrayof pins or bumpbonds98. FIG. 2A also illustrates a thin film of thermalinterface 102 applied to a top surface 101 of the electronic device 100.As shown in FIGS. 2A-2B, the heat rejecting device 104 or heat rejectoris configured to be coupled to the electronic device 100 via the thermalinterface 102. As stated above, the heat rejector 104 is preferably aheat sink which allows heat to transfer from the electronic device 100through the thermal interface 102. Alternatively, the heat rejector 104is any other heat exchanger. Alternatively, the heat rejector 104 is avapor escape heat exchanger described in co-pending U.S. patentapplication Ser. No. ______ filed ______ and entitled “______” which ishereby incorporated by reference. As shown in FIG. 2A, the heat rejector104 is coupled to the thermal interface 102, whereby heat produced bythe electronic device 100 is transferred by convection and conductionthrough the thermal interface 102 to the heat rejector 104.

[0025] The thermal interface 102 is preferably a phase change material,such as solder, whereby an attach layer 103 and the thermal interface102 preferably undergoes a phase change from solid to liquid when asufficient amount of heat is applied to it. Alternatively, the entirethermal interface 102 undergoes a phase change from solid to liquid whena sufficient amount of heat is applied to it. The thermal interface 102has small thermal resistance and allows shear without undergoingbilateral bending. For exemplary purposes, solder is referred to in thepresent description in relation to the thermal interface 102 althoughany other material which has a small thermal resistance and allows theheat rejector 104 to be easily removeable therefrom.

[0026] As shown in FIGS. 2A and 2B, the heat rejector 104 preferablyincludes a series of heating elements 106 in the bottom surface 108 ofthe heat rejector 104. Alternatively, as shown in FIGS. 2A and 2B, theheating element 106′ is on the upper surface 112 of the heat rejectordevice 104, whereby heat applied from the heating element 106′propagates through the heat rejector device 104 to the interface 108.Alternatively, as shown in FIGS. 2A and 2B, the heating element 106″ iswithin the heat rejector device 104, whereby heat applied from theheating element 106″ propagates through the heat rejector device 104 tothe interface 108. Alternatively, the heating elements 106 areconfigured within, on the top surface 112, on the bottom surface 108, orin any combination thereof, of the heat rejection device 104.

[0027] It is preferred that the heating elements 106 are electroniccircuits having one or more resistors, such as polysilicon resistors.Alternatively, the heating elements 106 are wire heaters. Alternatively,the heating elements 106 utilize any other appropriate components whichproduce an adequate amount of heat, as discussed below. Although severalheating elements 106 are shown in FIGS. 2A and 2B, any number of heatingelements 106 are contemplated within the present invention.

[0028] In addition, as shown in FIGS. 2-3, the heat rejection device 104includes two electrical contacts or terminals 110 on one of its surfaceswhich allow current to flow to the heating elements 106. Theseelectrical contacts 110 preferably have a dimension of approximately 100microns, although other sized contacts 110 are contemplated. Theseelectrical contacts 110 allow a brief, high-current to flow to theheating element 106, whereby the heating element 106 generates heatwhich passes to the thermal interface 102. The heating of heatingelement 106 sufficiently melts or “softens” the interface material 106without heating the entire electronic device 100. As a result, the heatrejector device 102 is able to be coupled to the electronic device 100without subjecting the electronic device 100 to unacceptabletemperatures which may damage the system.

[0029] Alternatively, the electrical contacts 110 are in the bottomsurface 108 or side surfaces or a combination of surface on the heatrejecting device 104, as shown in FIGS. 2A-2B. Although only twoelectrical terminals 110 are shown in FIGS. 2 and 3, any number ofelectrical contacts are alternatively present in the heat rejectiondevice 104. The heating elements 106 are preferably manufactured intothe surface of the heat rejector device 104 using standard bondingtechnology or other semiconductor wafer manufacturing methods which willnot be discussed in detail here. In addition, the electrical contacts110 are manufactured on or in the heat rejector device 104 using starteddeposition and lithography techniques. Alternatively, the electricalcontacts 110 are manufactured on or in the device 104 using screenprinting, solder re-flow or any other conventional process known by oneskilled in the art.

[0030] To couple the heat rejection device 104 to the thermal interface102 and eventually to the electronic device 100, a current is applied tothe heating element 106 through the electrical terminals 110. Thecurrent causes the heating element 106 to heat up to a temperature whichis preferably slightly higher than the melting point or phase changetemperature of the thermal interface 106 material. Alternatively, thetemperature of the heating element 106 is substantially higher than thephase change temperature of the thermal interface 102. Thus, the presentinvention utilizes the heat rejection device 104 as a source of heatwhich causes the heat rejection device 104 to form the engagement withthe interface. In addition, the characteristics of the thermal interface104 cause the thermal interface 104 to undergo a reverse phase change or“harden” when it is cooled or returns to its equilibrium state. Thehardening of the thermal interface 104 thereby secures and holds theheat rejection device 104 to the heat producing device 102.

[0031] In the preferred embodiment, the heating element 106 is heated toa predetermined temperature for a time period of a few microseconds to afew minutes, depending on a variety of factors. The temperature outputrequired from the heater element 104 depends on, but is not limited to,the type of thermal interface material 102 used, the amount of thermalinterface material between the electronic device 100 and heat rejector104 and the desired strength of the engagement between the electronicdevice 100 and heat rejector device 104. Additionally, the time periodof heating the thermal interface depends on, but is not limited to, thetype of thermal interface material 102 used between the electronicdevice 100 and heat rejector 104; the amount of current applied to theheater element 106; and the heat output capacity of the heater element106. Nonetheless, the heating element 106 is heated to the predeterminedtemperature before the electronic device 100 or the pins 99 and circuitboard 98 become warm.

[0032] In the preferred embodiment, current is steadily applied to theheating element 106 for an appropriate amount of time, depending onseveral factors, some of which are discussed above, to heat the heatingelement 106 to slightly above the phase change temperature of theinterface 102. Thus, the steadily increasing temperature of the heatingelement 106 is sufficiently large enough to melt the attach layer 103 ofthe interface 102 without allowing the heat to spread to the underlyingpackage and the surrounding components on the circuit board 99.Alternatively embodiment, current is applied to the heating element 106via the electrical terminals 110, whereby the heating element 106 isheat pulsed for a very brief time, ranging from a few microseconds to afew seconds, depending on the factors discussed above. In thisembodiment, the heat pulse from the heating element 106 is slow enoughto heat the attach layer 103 of the interface 102. However, the heatpulse is brief enough and low-enough in total energy that the activeregions of the electronic device 100 do not exceed their thermal budgetand thereby overheat. It should be noted that the nature of the heatrejection device 104 dissipates the heat created by the heating elements106. Thus, the timing of the heating pulse is set such that the thermalinterface 102 is sufficiently heated to undergo a phase change withoutthe electronic device 100 and heat rejector device 104 reaching anexcessively high temperature. In other words, the temporal duration ofthe heating pulse is substantially shorter than the thermal diffusiontime from the thermal interface 102 to the top surface 101 of theelectronic device 100, which is approximately 1 second.

[0033] It is preferred that the heating elements 106 are all heated tothe same temperature for the same amount of time. This method causes theinterface material 102 to uniformly undergo the phase change across theentire surface of the attach layer 103 of the thermal interface 102.Alternatively, the heating elements 106 heat the attach layer 103 of theinterface 102 in zones, such as quadrants. This alternative methodallows the entire interface 103 to then be formed incrementally inzones. This alternative method also allows large amount of heat to beapplied to a particular zone of the interface 102 in a single pulse,whereby the single pulse of heat has a temperature that is far below theamount that would overheat the electronic device 100.

[0034] The process of coupling the heat rejector device with theelectronic device will now be discussed in detail. FIGS. 3A and 3Billustrate a schematic of a preferred coupling method in accordance withthe present invention. As shown in FIGS. 3A and 3B, a mounting tool 201is in electrical contact with the terminals 210 on the lower surface 208of the heat rejection device 204. Alternatively, as discussed above andshown in FIGS. 2A and 2B, the electrical terminals are positioned on theside and/or top surfaces of the heat rejection device 204. In addition,a pair of spring members 208 are shown in FIGS. 3A and 3B, whereby thespring members allow the mounting tool 200 to press the heat rejectiondevice 212 to the thermal interface 202 and the electronic device 200.Similarly, the spring members 208 allow the mounting tool 201 to easilyremove the heat rejection device 204 from the thermal interface 202 andthe electronic device 200, as will be discussed below. It should benoted that the mounting tool 201 shown in FIGS. 3A and 3B is only forexemplary purposes and any different type of geometric arrangements ofthe mounting tool 201 to removeably couple the heat rejector device 204to the electronic device 200 is contemplated.

[0035]FIG. 4 illustrates a flow chart of the coupling method discussedin relation to FIGS. 3A and 3B according to the preferred embodiment ofthe present invention. The heat rejector device 204 itself, along withthe electrical contacts 210 and heating elements 206 is manufacturedusing known methods, as discussed above. Initially, in the preferredmethod, the electronic device 200 is coupled to the circuit board 99,whereby the array of pins 98 hold the electronic device 200 into thecircuit board 99 (step 300). Alternatively, the electronic device 200 iscoupled to the circuit board 99 after the thermal interface 202 isapplied to the electronic device 200 and the heat rejection device 204is also coupled thereto.

[0036] Following, the thermal interface 202 is preferably applied to thetop surface of the electronic device 200 (step 302). Alternatively, thethermal interface 202 is applied to the bottom of the electronic device200. Alternatively, the thermal interface 202 is applied to the topsurface and the bottom surfaces, individually or in combination on theheat rejection device 204. As stated above, the thermal interface 202 isapplied to the electronic device 200 using technologies and methodsknown in the art. The thermal interface 202, preferably solder, is in asolid state and is susceptible to phase change when heated to its phasechange temperature.

[0037] Once the electronic device 200 is prepared to engage the heatrejector device 204, the external mounting tool 201 (FIGS. 3A and 3B)moves the heat rejector device 204 to an predetermined position tocouple the heat rejector device 204 to the electronic device 200 (step304). Preferably, the appropriate position of the heat rejector device204 is above the electronic device 200. Alternatively, the appropriateposition of the heat rejector device 204 is adjacent or below theelectronic device 200.

[0038] The mounting tool 201 utilizes a power source 220 to move andposition the heat rejector device 204 as well as engage the heatrejector device 204 with the thermal interface 202. In addition, themounting tool 201 is coupled to a heating element power source 224 whichsupplies a current to the heating element 206 via the electricalcontacts 208. The electrical contacts 208 complete the electricalcircuit to heat the heating elements 206 and thereby engage the heatrejector device 204 with the electronic device 200. Alternatively, theelectrical contacts 210 are positioned on the top surface or adjacentsurface of the heat rejection device 204 as discussed above. The heatingelement power source 220 is preferably coupled to a control circuit 222which activates and controls the heating element 206. In addition, thecontrol circuit 222 controls the amount of time that the heating element206 is activated as well as whether the heating element 206 heats thethermal interface 202 gradually or in brief pulses.

[0039] As shown in FIG. 4B, the electronic device 200 is coupled to thecircuit board 99 when the heat rejection device 204 is removedtherefrom. Alternatively, the electronic device 200 is first removedfrom the circuit board 99 and the heat rejection device 204 is removedthereafter. the mounting tool 201 positions the heat rejector device 204in contact with the attach layer 203 of the thermal interface 202 (step306). Power is supplied from the heating element power source 224 andcontrolled by the control circuit 222, whereby current is supplied tothe heating element 206 for an appropriate amount of time, depending onthe factors discussed above (step 308). The current flowing through theheating element 206 causes the heating element 206 to produce asufficient amount of heat to raise the temperature of the thermalinterface 202 to above its phase change temperature (step 310). The risein temperature causes the thermal interface 202 to undergo a phasechange from a solid to a liquid. However, the heating element 206produces the adequate amount of heat in a brief enough period of timesuch that the heat does not pass to and thereby damage the electronicdevice 200, circuit board 99 or heat rejector device 204. As statedabove, the heat produced by the heating element 206 may be controlled bythe controller circuit 222 to be a gradual, uniform heating.Alternatively, the heat produced by the heating element 206 may becontrolled by the controller circuit 222 to be a brief pulses of apredetermined time duration. In addition, as discussed above, theheating element 206 may be configured to heat the thermal interface 202directly or alternatively in quadrants or zones.

[0040] The heat rejector device 204 is then pressed against theelectronic device 200 utilizing the springs 208, whereby the heatingelement 206 is at least partially embedded in the thermal interfacematerial 202 (step 312). The thermal interface 202, after transforminginto the liquid or softened state, allows the bottom surface of the heatrejector device 204 to be easily pressed into contact with the thermalinterface 202. After the appropriate amount of time of heating, thecontrol circuit 222 terminates supply of current to the heating element206, thereby allowing the heating element 206 to cool (step 314). Thetermination of current in effect lowers the temperature of the thermalinterface 202 below the phase change temperature. As the temperature ofthe thermal interface 202 drops below its phase change temperature, thethermal interface 202 undergoes a reverse phase change from a liquidback to a solid, preferably within a matter of seconds (step 316). Itshould be noted that the cool down time period varies depending on thetype of thermal interface 202, thickness of the thermal interface 202layer, as well as other factors discussed above. Alternatively, thethermal interface 202 rapidly cooled by a fan or other cooling device(not shown).

[0041] Once the thermal interface 202 cools back into the solid state,the heat rejection device 204 becomes engaged with and secured to theelectronic device 200. The properties of the solid phase thermalinterface 202 securely hold the heat rejection device 204 in place andallows heat to easily transfer from the electronic device 200 to theheat rejection device 204 due to the low thermal resistance of thethermal interface 202. Thereafter, the tool 200 releases the heatrejector device 204, whereby the rest of the assembly of the systemproceeds (step 316).

[0042] The process of removing the heat rejector device 204 from theelectronic device 100 will now be discussed. FIG. 5 illustrates a flowchart of the removal method discussed in relation to FIGS. 3A and 3Baccording to the preferred embodiment of the present invention. Toremove the heat rejector device 104 from the heat producing device 200,the mounting tool 201 moves and positions itself to engage the heatrejector device 204, as shown in FIG. 3B (step 400). Once the tool 201engages the heat rejector device 104, the electrodes 211 on the engagingarms of the tool 201 come into contact with the electrical terminals 210shown on the bottom surface of the heat rejector device 204. Power isthen supplied to the tool 201 from the power source 224, whereby currentpasses through the electrodes 211 to the heating element 206 via theelectrical terminals 110 (step 402).

[0043] The current flowing through the heating element 206 causes theheating element 206 to produce enough heat to raise the temperature ofthe thermal interface 202 above the phase change temperature (step 404).As stated above, the heat produced by the heating element 206 may becontrolled by the controller circuit 222 to be a gradual, uniformheating. Alternatively, the heat produced by the heating element 206 maybe controlled by the controller circuit 222 to be a brief pulses of apredetermined time duration. In addition, as discussed above, theheating element 206 may be configured to heat the thermal interface 202directly or alternatively in quadrants or zones.

[0044] The rise in temperature causes the thermal interface 202 toundergo a phase change from solid to liquid state. However, as statedabove, the heating element 206 produces enough heat in a brief enoughperiod of time such that the heat minimally passes or does not pass tothe electronic device 200 or heat rejector device 204. The phase changeof the thermal interface 202 into the liquid or softened state therebyreleases the heat rejector device 204 from the secured engagement (step406). The springs shown in FIGS. 3A and 3B along the mounting arms ofthe tool 201 in effect pull the heat rejector device 204 from thethermal interface 202, thereby disengaging the hear rejector device 204from the electronic device 200. Once the heat rejector device 204 isremoved from the electronic device 200, the heating element 206 is nolonger in contact with the thermal interface 202. Alternatively, afterthe appropriate amount of time that the thermal interface 102 has becomeliquid, the control circuit 206 terminates supplying the current to theheating element 106 and disengages the heat rejector device 104 from theelectronic device 100. The termination of heat supplied to the thermalinterface 102 lowers the temperature of the thermal interface 102,whereby the thermal interface 102 undergoes a phase change from a liquidback to a solid preferably within a matter of seconds (step 408).

[0045] The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modification s may be made inthe embodiment chosen for illustration without departing from the spiritand scope of the invention.

What is claimed is:
 1. A method of removeably coupling a heat rejectingdevice to a heat producing device comprising: a. configuring the heatrejecting device to include at least one heating element; b. applying athermal interface material to an interface surface of the heat producingdevice, a first surface of the heating rejecting device in contact withthe thermal interface material, the thermal interface materialconfigured to allow engagement and disengagement of the heat rejectingdevice above a predetermined temperature; and c. applying a current tothe at least one heating element for a predetermined amount of time,wherein the at least one heating element heats the thermal interfacematerial above the predetermined temperature.
 2. The method according toclaim 1 further comprising positioning the heat rejecting device at apredetermined location with respect to the heat producing device.
 3. Themethod according to claim 1 wherein the thermal interface materialundergoes a phase change between a first temperature below thepredetermined temperature and a second temperature above thepredetermined temperature.
 4. The method according to claim 3 whereinengagement of the heat rejecting device with the heat producing devicefurther comprises pressing the heat rejecting device and the thermalinterface material against one another until the temperature of thethermal interface material is substantially at the first temperature. 5.The method according to claim 3 wherein disengagement of the heatrejecting device with the heat producing device further comprisesremoving the heat rejecting device and the thermal interface materialagainst one another when the temperature of the thermal interfacematerial is substantially at the second temperature.
 6. The methodaccording to claim 1 wherein the at least one heating element ispositioned on the first surface of the heat rejecting device.
 7. Themethod according to claim 1 wherein the at least one heating element ispositioned on a heat rejecting device surface opposite of the firstsurface of the heat rejecting device.
 8. The method according to claim 1wherein the at least one heating element is positioned within the heatrejecting device.
 9. The method according to claim 1 wherein the atleast one heating element heats the thermal interface material inpredetermined zone locations.
 10. The method according to claim 1wherein the at least one heating element applies heat to the thermalinterface material in a substantially uniform manner.
 11. The methodaccording to claim 1 wherein the at least one heating element appliesheat to the thermal interface material by a plurality of heat pulses,each heat pulse being of a predetermined time duration.
 12. The methodaccording to claim 1 further comprising configuring the heat rejectingdevice to include at least one electrical contact positioned on apredetermined surface, wherein the current is applied through the atleast one electrical contact.
 13. A heat rejector device configured tobe removeably coupled to a thermal interface material, the thermalinterface material configurable to engage and disengage the heatrejector device above a predetermined temperature, the heat rejectordevice comprising at least one heating element, wherein a currentapplied to the at least one heating element for a predetermined amountof time produces an adequate amount of heat in the at least one heatingelement to heat the thermal interface material above the predeterminedtemperature.
 14. The heat rejector device according to claim 13 whereinthe thermal interface material undergoes a phase change between a firsttemperature below the predetermined temperature and a second temperatureabove the predetermined temperature.
 15. The heat rejector deviceaccording to claim 14 wherein the thermal interface material engages theheat rejecting device by being pressed against the heat rejecting deviceuntil the thermal interface material reaches to the first temperature.16. The heat rejector device according to claim 14 wherein the thermalinterface material disengages the heat rejecting device by removing theheat rejecting device and the thermal interface material from oneanother when the thermal interface material is at the secondtemperature.
 17. The heat rejector device according to claim 13, whereinthe at least one heating element is configured to be in contact with thethermal interface material.
 18. The heat rejector device according toclaim 13 wherein the at least one heating element is positioned on asurface of the heat rejector device opposite of the thermal interfacematerial.
 19. The heat rejector device according to claim 13 wherein theat least one heating element is positioned within the heat rejectordevice.
 20. The heat rejector device according to claim 13 wherein theat least one heating element heats the thermal interface material inpredetermined zone locations.
 21. The heat rejector device according toclaim 13 wherein the at least one heating element applies heat to thethermal interface material in a substantially uniform manner.
 22. Theheat rejector device according to claim 13 wherein the at least oneheating element applies heat to the thermal interface material by aplurality of heat pulses, each heat pulse being of a predetermined timeduration.
 23. The heat rejector device according to claim 13 furthercomprising at least one electrical contact positioned on a predeterminedsurface, wherein the current is applied through the at least oneelectrical contact.
 24. A heat rejector device coupled to an interfacematerial, wherein the heat rejector device is secured to the interfacematerial in a first phase state and configured to be removeable from theinterface material in a second phase state, the heat rejector devicecomprising at least one heating element for applying a predeterminedamount of heat to the interface material such that the interfacematerial undergoes a phase change from the first phase state to thesecond phase state in response to the predetermined amount of heatapplied thereto by the at least one heating element.
 25. The heatrejector device according to claim 24 wherein the interface material isin the first phase state when below a predetermined phase changetemperature.
 26. The heat rejector device according to claim 25 whereinthe interface material is in the second phase state when above thepredetermined phase change temperature.
 27. The heat rejector deviceaccording to claim 24 wherein the interface material undergoes the phasechange between the first phase state and the second phase state withinan appropriate amount of time.
 28. The heat rejector device according toclaim 24 wherein the at least one heating element heats the interfacematerial in predetermined zone locations.
 29. The heat rejector deviceaccording to claim 24 wherein the at least one heating element appliesheat to the interface material in a substantially uniform manner. 30.The heat rejector device according to claim 24 wherein the at least oneheating element applies heat to the interface material by a plurality ofheat pulses, each heat pulse being of a predetermined time duration. 31.The heat rejector device according to claim 24 wherein the at least oneheating element is configured to be in contact with the interfacematerial.
 32. The heat rejector device according to claim 24 wherein theat least one heating element is positioned on a surface of the heatrejector device opposite of the interface material.
 33. The heatrejector device according to claim 24 wherein the at least one heatingelement is positioned within the heat rejector device.
 34. The heatrejector device according to claim 24 further comprising at least oneelectrical contact positioned on a predetermined surface, wherein thecurrent is applied through the at least one electrical contact.
 35. Anassembly for removeably coupling a heat rejecting device to a heatproducing device, wherein a thermal interface material having apredetermined phase change temperature is applied between the heatrejecting device and the heat producing device, the assembly comprising:a. means for holding an interface surface of the heat rejecting devicein contact with the thermal interface material, wherein at least oneheating element configured on the interface surface is in contact withthe thermal interface material; and b. means for energizing the at leastone heating element for a predetermined amount of time, wherein the atleast one heating element transforms the thermal interface material toundergo a phase change the thermal interface material substantiallyreaches the predetermined phase change temperature.
 36. A method ofremoveably coupling a heat rejecting device with a heat producingdevice, wherein a thermal interface material having a predeterminedphase change temperature is between the heat rejecting device and theheat producing device, the method comprising: a. configuring the heatrejecting device to include at least one heating element; and b.energizing the at least one heating element for a predetermined amountof time, wherein a current applied to the at least one heating elementheats the at least one heating element until the thermal interfacematerial substantially reaches the predetermined phase changetemperature.